The document US 2009/0116114 A1 discloses dichroic filters for merging blue light from a light-emitting diode (LED) and the yellow light from a phosphor to form white mixed light. In this case, the blue light from the LED is transmitted and the yellow light from the phosphor is reflected.
The document US 2010/0156958 A1 discloses in FIG. 8 a projection system 800 comprising a lighting device for illuminating the two image generating units 820, 822. The lighting device comprises a lamp 802, in particular a high-pressure lamp, the white light from which is filtered sequentially into colored light portions with the aid of a rotating color filter wheel 806. A yellow notch filter 818 disposed downstream of the color filter wheel 806 filters the yellow light portion from the previously filtered colored light portions in order thus to improve the color space.
The document US 2012/0274908 A1 discloses a lighting device for a projector. The lighting device comprises a high-pressure mercury vapor lamp and at least in each case one laser that emits red light and one laser that emits green light. The red light laser is intended to compensate for the excessively small red light portion of high-pressure mercury vapor lamps. A yellow notch filter serves for suppressing the yellow light portion, which is very high in the case of high-pressure mercury vapor lamps, and thus for setting a white point that is correct for the projection.
The document US 2013/062637 A1 discloses a semiconductor light source comprising a phosphor layer, in particular an LED in a housing comprising a phosphor layer. A double notch filter layer transmits desired wavelengths, such as green and red, and reflects others, such as yellow and blue, for example, back to the phosphor.
What is disadvantageous about currently available phosphors is that the size of the addressable color space is smaller than desired. These phosphors are not well suited to many projection applications, e.g. home cinema, simulation. A color space is sought which corresponds approximately to Rec. 709 for the green and red color channels (sRGB color space). For this, the so-called dominant wavelength of green phosphors, that is to say in the green spectral range, is usually too long and the dominant wavelength at least of efficient red phosphors, that is to say in the red spectral range, is too short. Red phosphors having a suitable dominant wavelength generally have a relatively low conversion efficiency. The dominant wavelength of light having a light color (colored light) is defined in the CIE chromaticity diagram (standard chromaticity diagram) by the point of intersection between the straight line, extended from the white point via the determined color locus of the colored light, and the spectrum locus of the closest edge of the CIE chromaticity diagram.
The document CN 102385233 A discloses a lighting device for a projector comprising a pump laser, a phosphor wheel for the wavelength conversion of the pump laser light into conversion light, and a filter wheel, for spectrally filtering the conversion light. The filter wheel and the phosphor wheel are arranged on a common axis and thus rotate at the same speed. The pump laser light is reflected onto the phosphor wheel with the aid of a dichroic mirror. By contrast, the conversion light reflected back from the phosphor wheel passes through the dichroic mirror and then impinges on the filter wheel. Through a transparency segment in the phosphor wheel, the pump laser light can pass through the phosphor wheel in a spectrally unchanged manner and is fed to the dichroic mirror via a so-called wrap around loop and is combined with the conversion light path.
The use of an additional filter wheel upstream of the integrator within a DLP projector causes additional costs, additional space requirement and possibly additional complexity in the driving of the filter wheel and the synchronization with the phosphor wheel.